Resilient structures for mattress cores are commonly constructed using various configurations of padded coil springs and/or synthetic foam materials, for example. Resilient structures such as batts made from synthetic fibers have been used as low cost alternatives to coil spring and foam structures in mattress cores and furniture upholstery. However synthetic fibers such as nylon and polyester have tendency to rebound to an original shape after compression due to inherent plastic memory in the fibers. Restraining the compressed fiber structure in a container such as mattress cover has resulted in unevenness and eventual deterioration of the resilient structure.
Various techniques have been used to overcome the plastic memory of synthetic fibers to construct a batt having a desired density. For example, U.S. Pat. No. 4,753,673 entitled Method for Forming a Vacuum Bonded Non-Woven Batt describes forming a vacuum bonded non-woven batt by blending multiple polymer fibers in which on type of fiber has a relatively low melting temperature and another type of fiber has a relatively high melting temperature. The blended fibers are formed into a thick web or a multi-layered web which is then compressed by vacuum while applying heat to release the plastic memory of the lower melting temperature fiber. This fuses the two types of fibers to form a relatively high density resilient batt having interconnected fused fibers. However, the previously known resilient structures made from fiber batts have not provided a desired degree compression resistance, comfort, durability.
Resilient structures made from blended fibers have been enhanced to increase resiliency in strategic locations by imbedding coil springs in the fiber matt. For example, U.S. Pat. No. 6,077,378 entitled Method of Forming Densified Fiber Batt with Coil Springs Interlocked Therein describes a densified fiber batt core including low melt fibers which when heated to the melting point and then cooled, intersect and interlock with coil springs. The coil springs function as an integral part of the fiber batt. However, portions of the fiber batt that lack imbedded coil springs may lack compression resistance or resiliency. Moreover, differences between the compressibility of fiber portions and spring portions of the structure may cause the springs to become unlinked from the fibers and cause premature deterioration of the structure.